Mandatory insurance. Those are two words that I hate to hear when I’m renting a car outside the U.S. On Thursday night, I spent an hour and a half in a Thrifty Rent a Car location near the airport in San Jose, Costa Rica, trying to understand how an eight-day rental that I expected to pay $394 for was somehow going to cost me either $786 or $946. I’m an experienced traveler and I should have known better. Here’s how I got scammed and how you can avoid the same fate.

I spent a huge amount of time shopping around for a deal on a rental car for an eight-day trip to Costa Rica and the best price I found was through Thrifty, which quoted me a price of $394 for an automatic transmission SUV. By American standards, this was no bargain, but in Costa Rica during the high season it was the best deal I could find.

I received a confirmation email from Thrifty that listed my estimated “mandatory charges” (base rental price, one-way drop off surcharge, vehicle license fee) plus optional charges (booster seat for child), and then the “estimated grand total” price. Two days before we arrived in country, the local branch also confirmed the reservation and the price via email. Even in the fine print of both emails there is no mention of any additional charges or mandatory insurance costs.We arrived at the Thrifty location near the San Jose airport on Thursday night and, despite the fact that there was only one person in front of us in line, we waited 40 minutes to find out that our $394 rental car was actually going to cost $786 if we opted for the lowest possible level of insurance or $946 if we chose the more comprehensive coverage. We spent nearly another hour unsuccessfully trying to untangle the mess and it quickly became clear why we’d waited so long to get to the counter in the first place: everyone was arguing with them about the same issue as they were shocked to find double the rates they expected.

I thought it was a scam because the agent was jotting down all these prices on a scrap of paper as though he was making it up as he went along. I’ve been hit up for mandatory insurance in other countries before but those costs were more an annoyance than the budget buster this was. So I walked out and tried two other rental car places, both of which quoted similar rates.

Rather than pay nearly $100 per day to rent the car, we took a cab to our hotel and I studied the confirmation email from Thrifty. Even in the fine print and “terms and conditions” of the confirmation email there was no mention of the mandatory insurance. I called Thrifty to complain and all they could manage was their contention that my rate was only an “estimated grand total” and not an “actual grand total.”

I went back to Thrifty’s website and tried to make a new reservation, this time studying all the fine print in the terms and conditions section and still couldn’t find any mention of the huge mandatory insurance cost.

I also checked the section on car rentals in my guidebook (Frommer’s) and there is no explicit warning about the exorbitant mandatory insurance, only a boilerplate sentence about checking to see if your existing insurance in the U.S. will cover you in Costa Rica.

I’m sure that Thrifty isn’t the only company guilty of this sort of bait-and-switch pricing, and as an experienced traveler, who has rented cars in a variety of countries, I should have clarified that their “grand total” estimate really was going to be the grand total. But I took the term “grand total” at face value. Next time I’ll know better and you should too. In the meantime, which way to the San Jose bus station?